Iron stabilizers for 3-isothiazolones

Abstract: A method of preparing a stable, dilute aqueous solution of at least one 3-isothiazolone compound comprising 5-chloro-2-methyl-3-isothiazolone, the concentration of said compound(s) in said solution being about 0.5 to 5% by weight based on solution, comprising introducing about 0.1 to 5% by weight based on said solution, of a ferric salt as the stabilizer is disclosed. Dilute aqueous solutions of about 0.5 to 5.0 parts by weight of at least one 3-isothiazolone compound comprising 5-chloro-2-methyl-3-isothiazolone, about 0.1 to 2.5 parts by weight of a stabilizing, water soluble, non-chelated ferric salt, and about 92 to 99 parts by weight of aqueous solvent, are also disclosed.

Description: This invention relates to the stabilization of dilute solutions of 3-isothiazolones, that is to say, solutions containing from 1 to 5% by weight of the active ingredient 3-isothiazolone compounds (hereafter "active ingredient" or AI) are a very important class of microbicides. Several species have been commercialized and are widely used to inhibit the growth of bacteria, fungi and algae. Among the most important species are 2-methyl-3-isothiazolone ("MI"), 5-chloro-2-methyl-3-isothiazolone ("CMI"), and especially mixtures thereof. A 3/1 weight ratio mixture of CMI and MI is used in a wide variety of commercial applications around the world CMI is naturally unstable and much research has been devoted to stabilizing it in four quite separate conditions: firstly as the isolated compound itself; secondly as an aqueous concentrate containing from about 14 to 25% by weight of the active ingredient; thirdly as a dilute aqueous solution containing from about 1 to 5% by weight of the AI and which are intended to be further diluted during use to a much lower AI concentration; and lastly as a dilute end use solution containing the AI in amount substantially less than 1% by weight.. To stabilize the isolated compound itself, U.S. 4,150,026 teaches making metal salt complexes of the isothiazolone. These complexes are said to greatly enhance the thermal stability of the solid isothiazolone, as compared with the corresponding uncomplexed compound. No mention is made of the stabilization of the isothiazolone in aqueous solution whether as a concentrate, as a dilute solution, or as an end use dilute solution. U.S. 3,870,795 teaches the stabilization of aqueous concentrates of 3-isothiazolone,, i.e containing 25% AI, against chemical decomposition by adding a metal nitrite or nitrate. Among the useful nitrates are those of sodium, potassium, calcium, magnesium, ferric, ferrous, nickel, zinc, barium, manganese, silver, cobalt, and the like, and among the useful nitrites are those of sodium, potassium, calcium, magnesium, and the like. The '795 patent discloses that other common anions, including carbonates, sulfates, chlorates, perchlorates, and chlorides, are surprisingly ineffective. The '795 patent also teaches that the isothiazolone can be an aqueous solution of the compound itself, or of the complexes. According to '795, neither the concentrates, nor the complexes, nor non-aqueous solutions of either the compounds or the complexes, and containing 25% by weight of the AI are stable unless stabilized with nitrates or nitrites. The patent is not concerned with the stabilization of dilute solutions. All of the '795 examples are directed to 25% solutions of the compounds or the complexes thereof. U.S. 5,160,527 , which concerns the stabilization of isothiazolones at end use concentrations, i.e. in a particular locus, discloses that, in such loci and at the extreme dilutions involved, the isothiazolone active ingredients can be stabilized by the addition to the end use solution of a metal salt (Cu, ferrous, ferric, zinc, manganese, magnesium) of an organic carboxylic acid of at least six carbon atoms, (which are water insoluble), or a chelating anion selected from EDTA, 8-hydroxyquinolinate, gluconate, o-phenanthroline, quinolinate, N,N-bis(2-hydroxy-5-sulfobenzyl)glycine, lignosulfonate polymers, and polyacrylates. The use dilutions suggested by the '527 patent, comprise loci which contain destabilizing components such as amines, reducing agents (e.g., bisulfites), and fuel. These "destabilizing components" react with the AI. The patent does not teach any method of stabilizing aqueous solutions containing higher amounts of the AI, ie in the range 1 to 5%. U.S. 5,118,699, teaches the stabilizing effect of hydrazide compounds on isothiazolones present in metal working fluids and similar loci containing components antagonistic to the AI. U.S. 5,142,058, teaches the stabilizing effect of alkyl halohydantoins and the like in similar antagonistic loci, i.e., at end use dilutions. Neither patent relates to stability of the AI in dilute aqueous solutions. For such dilute solutions there are two conventional methods of stabilization. The first is to use high ratios (e.g., about 15:1) of Mg(NO 3 ) 2 to AI. Mg(NO 3 ) 2 is not effective at lower ratios, i.e., about 1:1. The second is to use a cupric salt as the stabilizer. The cupric salt is conventionally used at a ratio of about 1:10 to AI since only very small amounts of cupric ion are necessary for effective stabilization. The reason use of cupric ion is preferred in industrial situations is that too much nitrate salt is disadvantageous in certain applications or loci. However, the cupric stabilizer has recently come under question because of government regulatory limits in certain countries on the amount permitted in water discharge streams. Since dilute solutions have certain advantages over the concentrates (ease of handling, reduced potential for sensitization of workers, and greater flexibility of formulations), it became necessary to find an alternative stabilization method to the cupric ion or high levels of nitrates. In accordance with the present invention, and contrary to some of the findings described above, we have found that non-chelated, water-soluble ferric salts are surprisingly effective stabilisers for CMI in dilute aqueous solution, i.e. aqueous solutions containing from 1 to 5% active ingredient. Accordingly, there are now provided, in accordance with this invention, dilute aqueous solutions of 5-chloro-2-methyl-3-isothiazolone containing said 5-chloro-2-methyl-3-isathiazolone, and optionally one or more other isothiazolones, in a total amount of from 1.0 to 5.0% by weight, based on the weight of the solution, said solution also containing, as a stabiliser, from 0.1 to 5% by weight, based on the the total weight of the solution, of a non-chelated, water soluble ferric salt, preferably ferric chloride, ferric nitrate, ferric sulfate, ferric bromide, ferric acetate or ferric iodide , most preferably ferric sulfate. Preferred solutions according to the invention contain from about 1.4 to 1.6% by weight, more particularly 1.5% by weight, of isothiazolone and from about 0.1 to about 2.5% by weight, of the ferrice salt. In the dilute aqueous solutions of the invention, the solvent is generally exclusively water; however certain organic solvents can be employed in addition to water, although only at relatively low levels. Such solutions are also referred to herein as "aqueous". Suitable organic solvents are ethylene glycol, diethylene glycol, diethylene glycol butyl ether, propylene glycol, dipropylene glycol, dipropylene glycol butyl ether, polypropylene glycol, polyethylene glycol, methoxy ethanol, and the like, and the amounts used can be up to 30% by weight based on the dilute solution. The preferred solvent system is all water and no organic solvent. It has also been surprisingly found that it is possible to extend the stabilizing effect of low levels of ferric ion by the addition of small amounts of an oxidant. Suitable oxidants are sodium chlorate (which is preferred) and N-bromosuccinimide. The amount of oxidant used is preferably about 0.1 % to about 5 % by weight, more preferably about 0.5 % to about 1.5 % by weight, based on dilute aqueous solution. When slightly higher levels of ferric salt are used, use of the oxidant is not necessary. It is also preferred to add a small amount of acid to prevent precipitate formation, which can be a problem in certain cases (although the precipitate does not affect the stability of the system). Addition of acid does not negatively affect the stabilizing action of the ferric salt, and is compatible with the isothiazolone. Any acid which effectively lowers the pH of the stabilized isothiazolone solution may be used. Preferred acids are hydrochloric acid, nitric acid, and sulfuric acid The amount of acid required will vary depending upon the initial pH of the stabilized isothiazolone solution and the proposed end use of the isothiazolone, amongst other factors, but will generally be used in an amount sufficient to lower the initial pH of the stabilized isothiazolone solution (ie the pH at the time of preparation of the solution) to at least about 1.5, and preferably to between 1.0 and 1.4. The preferred acid is hydrochloric. The dilute solutions of the invention can be prepared from concentrates by adding water and ferric salt. Typical concentrates comprise about 14% AI and 14-15% Mg(NO 3 ) 2 in an aqueous solution. Dilute solutions prepared from such concentrates generally contain from 0.5 to 6% by weight of Mg(NO 3 ) 2 . The solutions can also be prepared by dilution of a salt free, i.e., Mg(NO 3 ) 2 - free, solution of AI in a glycol. The dilute solutions can also be prepared directly from salt-free technical AI, aqueous solvent (eg water), and ferric salt. The compositions of this invention are suitable for a wide variety of applications in a number of industries. A further aspect of the invention is a method of preventing or inhibiting the growth of bacteria, fungi or algae in a locus susceptible or subject to contamination thereby, comprising introducing into or onto said locus, in an amount effective to inhibit said growth, a composition as defined above. The dilute solutions are further diluted when introduced into, onto, or at a locus to be protected The loci in which the use dilutions are particularly useful are water treatment, especially in pulp and paper processing and in cooling towers. Other examples of loci are adhesives, sealants, agriculture adjuvant preservation, construction products, cosmetics and toiletries, disinfectants and antiseptics, emulsions and dispersions, formulated consumer and industrial products, industrial processing, laundry, leather and leather products, lubricants and hydraulic aids, medical devices, metalworking and related applications, odor control, paints and coatings, petroleum refining and fuels, photographic chemicals, printing, sanitizers, soaps and detergents, textiles and textile products and textile processing, water purification and wood applications. The ferric ion does not function to stabilize AI in the loci when diluted and introduced in these loci (ie at use dilution rather than in the form of a dilute solution). Other stabilizers are needed in certain of these loci, especially metal working fluids, shampoos, caulks, paints, other latices, and the like. It is known in the art that the performance of microbicides may be enhanced by combination with one or more other microbicides. Thus, other known microbicides may be combined advantageously with the composition of this invention. The following specific examples are presented to illustrate various aspects of the invention but are not to be construed as limitations thereof. All parts and percentages are by weight unless otherwise specified, and all reagents are of good commercial quality unless otherwise specified The relative concentration of the active ingredient was determined by reverse phase high performance liquid chromatography (HPLC), utilizing an ultraviolet detector, unless otherwise noted Adequate stabilization was defined as 60% of the isothiazolone remaining after 4 weeks at 55°C. In all the aqueous solutions of the Examples the solvent is water only. EXAMPLE 1 (Comparative) This example illustrates the effect of increasing dilutions with water of a "concentrate," i.e., an aqueous solution containing 25% isothiazolone and 25% magnesium nitrate stabilizer. The isothiazolone was a 3:1 by weight mixture of CMI and MI. The dilutions shown in Table 1 were prepared and stored at 55°C for 8 weeks and analyzed for CMI at the time intervals of 1, 2, 3, 4, 6, and 8 weeks. % AI % Mg(NO 3 ) 2 % CMI Remaining Weeks at 55°C 1 2 3 4 6 8 25 25 93 86 76 61 0 - 12 12 84 74 61 45 0 - 6 6 77 66 51 33 0 - 3 3 55 38 21 7 0 - 1.5 1.5 31 0 - - - - These data indicate that conventional magnesium nitrate stabilizer, used at a 1/1 weight ratio to 3-isothiazolone, becomes less effective with increasing dilution with water. EXAMPLE 2 - Stabilizing Effect of Salts of Various Metal Ions Dilute solutions (1.5% CMI/MI, 3:1) with 1% of various metal salts in water were prepared and evaluated for stabilization of the active ingredient. The samples were stored at 55°C for 2 weeks. Analyses were performed at the time of preparation and after storage using a UV absorption method. The results are reported as percent AI lost. Stabilizer (1%) % Isothiazolone lost None ( - control) 82 Cupric nitrate ( + control) 0 Ferric sulfate (Invention) 0 Ferrous sulfate (Comparative) 74 Zinc sulfate (Comparative) 82 Zirconium sulfate (Comparative) 79 Chromium nitrate (Comparative) 73 Cerium (IV) sulfate (Comparative) 69 Cobalt sulfate (Comparative) 77 Nickel sulfate (Comparative) 77 Manganese sulfate (Comparative) 85 Lead nitrate (Comparative) 64 Lanthanum sulfate (Comparative) 84 Thorium sulfate (Comparative) 74 Tin (II) chloride (Comparative) 97 Bismuth tartrate (Comparative) 78 This example demonstrates that ferric ion is exceptional in that it functions as an effective stabilizer of dilute solutions when added at a 1% based on weight of solution, whereas other metals, except for copper, do not. This example also demonstrates that nitrate ion when added at 1% based on weight of solution is not effective as a stabilizer in dilute solutions, either, except when used as a counterion with ferric or cupric cations. EXAMPLE 3 This example demonstrates the unusual effectiveness of ferric cation as a stabilizer of isothiazolone in dilute aqueous solutions compared to other cations disclosed as stabilizers for concentrates in the '795 patent. In this example, nitrates of the various cations were compared at 1.5% concentration in solutions containing about 1.5% isothiazolone in water. The % CMI remaining after 1 and 2 weeks was measured and reported in Table 3. Stability of dilute (1.5%) aqueous solutions of AI containing metal nitrate salts Invention/Comparative Stabilizer (1.5%, anhyd) Weeks (at 55°C) %MI %CMI %CMI remaining Invention Fe(NO 3 ) 3 0 0.41 1.32 100 1 0.41 1.32 100 2 0.41 1.33 100 4 0.42 1.34 100 Comparative Mg(NO 3 ) 2 0 0.35 1.15 100 1 0.34 0.73 63 2 0.34 0.72 63 4 0.31 0.44 38 Comparative Ni(NO 3 ) 2 0 0.35 1.10 100 1 0.36 0.69 63 2 0.35 0.68 62 4 0.33 0.44 40 Comparative Zn(NO 3 ) 2 0 0.35 1.15 100 1 0.35 0.67 58 2 0.34 0.66 57 4 0.32 0.44 38 Comparative Mn(NO 3 ) 2 0 0.32 1.03 100 1 0.32 0.74 72 2 0.32 0.73 71 4 0.28 0.46 45 Comparative NaNO 3 0 0.38 1.22 100 1 0.37 0.75 61 2 0.36 0.74 61 4 0.33 0.46 38 Comparative Ca(NO 3 ) 2 0 0.38 1.23 100 1 0.37 0.80 65 2 0.36 0.80 65 4 0.35 0.49 40 Control (-) no stabilizer 0 0.35 1.14 100 1 0.23 0.00 0 2 0.23 0.00 0 4 0.17 0 0 EXAMPLE 4 The effect of varying the anion of the soluble ferric salt as well as the concentration of the salt was determined. A series of 1.5% isothiazolone (3:1 mixture CMI and MI) dilute aqueous solutions was prepared by diluting a concentrate based on 14% of the 3:1 mixture of CMI and MI containing 15% Mg(NO 3 ) 2 stabilizer. The resultant dilute aqueous solution samples were stabilized by the addition of varying amounts of the ferric salts listed in Table 4, which shows the results. All the samples, including the negative control, contained about 1.6% residual Mg(NO 3 ) 2 (from the initial concentrate); this alone is insufficient for adequate stabilisation, as seen in the control result below and also from Table 1. % Stabilizer % CMI Remaining Weeks 1 3 5 8 Control (negative) 92 59 30 - 0.01 Ferric Chloride 100 81 48 15 0.05 Ferric Chloride 100 96 87 75 0.10 Ferric Chloride 100 100 100 100 0.15 Ferric Chloride 100 97 94 91 0.20 Ferric Chloride 100 97 96 93 0.25 Ferric Chloride 100 96 92 92 0.01 Ferric Nitrate 100 78 44 13 0.05 Ferric Nitrate 99 95 80 56 0.10 Ferric Nitrate 100 97 86 71 0.15 Ferric Nitrate 100 98 90 80 0.20 Ferric Nitrate 100 97 92 87 0.25 Ferric Nitrate 100 100 96 95 0.01 Ferric Sulfate 100 78 42 9 0.05 Ferric Sulfate 100 94 74 47 0.10 Ferric Sulfate 100 90 75 59 0.15 Ferric Sulfate 100 95 84 75 0.20 Ferric Sulfate 100 97 88 77 0.25 Ferric Sulfate 100 98 96 100 These data show that ferric cation is an effective stabilizer at very low concentrations, regardless of the anion. EXAMPLE 5 In the ferric salt-containing samples of the previous examples, a reddish-brown precipitate was observed after a few weeks storage at 55°C. While this precipitate represents a small amount of material, and in no way interferes with the stabilizing action of the ferric ion, the presence of precipitate is generally considered undesirable by commercial users of biocide formulations. The precipitate was found to result from hydrolysis of hydrated ferric ion. Such precipitates can be observed to form upon high temperature storage of aqueous solutions of ferric salts in the absence of isothiazolones. Dilute aqueous solutions of 1.5% isothiazolone were prepared by dilution with water of commercial 14% isothiazolone concentrates which had been stabilized with 15% magnesium nitrate. Ferric chloride (0.25%) was added to stabilize samples A and B. A sample (C) without added ferric chloride served as the control. In sample A the pH was lowered with HCl. A (-) indicates sample is clear and free from precipitate. A (+) indicates sample has a red-brown precipitate. A (*) indicates yellow precipitate as result of AI decomposition. Effect of pH Adjustment Sample Weeks Stored at 55°C 0 2 4 8 A (pH adjusted) Appearance - - - - pH 1.0 0.8 0.8 0.7 % CMI Remaining 100 95 93 89 B (Not Adjusted) Appearance - + + + pH 1.5 1.0 1.2 1.2 % CMI Remaining 100 97 96 94 C (Control) Appearance - * * * pH 1.5 1.3 1.5 1.4 % CMI Remaining 100 79 60 0 These data show that the formation of the red-brown precipitate is prevented by acidifying dilute aqueous solutions containing ferric ion stabilizer. EXAMPLE 6 This example illustrates the use of small amounts of an oxidant to enhance the stabilizing action of ferric ion, thereby allowing use of extremely low levels of ferric salt. To successive 1.5% isothiazolone dilute solutions (CMI/MI, 3:1 mixture) was added 1% sodium chlorate; 0.1% ferric sulfate; and 0.1% ferric sulfate plus 1% sodium chlorate. The positive control was commercially available 1.5% isothiazolone dilute solution with added copper as a stabilizer. The negative control was 1.5% AI dilute solution without any added stabilizer. The results are reported in Table 6 as percent CMI remaining. % CMI Remaining Weeks 1 2 5 6 Control (positive - Cu stabilised) 100 97 86 88 Control (negative - no stabiliser) 0 - - - 1% NaClO 3 0 - - - 0.1% Fe 2 (SO 4 ) 3 99 39 - - 0.1% Fe 2 (SO 4 ) 3 + 1% NaClO 3 98 96 71 72 This example demonstrates that ferric salts can be used at very low levels to stabilize AI when an oxidant is used. In summary of the above data, ferric salts have been discovered to be effective stabilizers for dilute aqueous solutions of isothiazolone. The stabilization is independent of the anion chosen, so long as the ferric salt is soluble in the system. While this invention has been described in sufficient detail for those skilled in the art to be able to make and use it, various alternatives, modifications, and improvements should become apparent from the foregoing disclosure.

Claims: A dilute aqueous solution of 5-chloro-2-methyl-3-isothiazolone containing said 5-chloro-2-methyl-3-isothiazolone, and optionally one or more other isothiazolones, in a total amount of from 1.0 to 5.0% by weight, based on the weight of the solution, said solution also containing, as a stabiliser, from 0.1 to 5% by weight, based on the total weight of the solution, of a water soluble, non-chelated ferric salt other than a ferric salt of an organic carboxylic acid with 6 or more carbon atoms. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in claim 1, wherein the stabiliser is ferric chloride, ferric sulfate, ferric nitrate, ferric acetate, ferric iodide or ferric bromide, preferably ferric sulfate. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in claim 1 or 2, wherein the concentration of the 5-chloro-2-methyl-3-isothiazolone, plus other isothiazolones, if any, is in the range 1.4 to 1.6% by eight, based on the total weight of the solution. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in claim 1, 2 or 3, wherein the concentration of the ferric salt is in the range 0.1 to 2.5% by weight, based on the total weight of the solution. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in any one of claims 1 to 4, wherein the non-chelated, water soluble ferric salt is present in an amount of from 0.1 to 2.5% by weight, based on the total weight of the solution. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in any one of claims 1 to 5, wherein the pH of the solution is less than 1.5, preferably in the range 1.0 to 1.4. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in any one of claims 1 to 6, additionally containing from 0.1 to 5% by weight, preferably 0.5 to 1.5% by weight, based on the total weight of the solution, of an oxidant. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in Claim 7, wherein the antioxidant is N-bromosuccinimide or sodium chlorate. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in any one of the preceding claims, wherein the 5-chloro-2-methyl-3-isothiazolone is present in admixture with 2-methyl-3-isothiazolone in a weight ratio of 3:1. An aqueous solution of 5-chloro-2-methyl-3-isothiazolone as claimed in any one of the preceding claims, additionally containing magnesium nitrate, preferably in an amount of from 0.5 to 6% by weight, based on the total weight of the solution.

Inventors: MATTOX JOHN ROBERT, MATTOX, JOHN ROBERT
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 1994
Main classification: A01N43
IPC codes: A01N43, C09K15, A01N25, C07D275